Predation is an important source of natural selection on prey species and has resulted in adaptations such as antipredator vocal signals,which can alert others to the presence of predators and solicit cooperative atta...Predation is an important source of natural selection on prey species and has resulted in adaptations such as antipredator vocal signals,which can alert others to the presence of predators and solicit cooperative attack.Although vocal alarm signals of birds have been well studied,they are poorly known in tropical African species.To address this lack of information,the antipredatory signals and responses of two lapwings(Wattled Lapwing Vanellus senegallus and Spur-winged Lapwing Vanellus spinosus)to potential predators were investigated using data collected from focal observation,distance measurements,focal recordings,and playback experiment.The lapwing calls elicited to predators were classified as alarm or mobbing calls based on whether the calls elicited alert behavior or attack from other lapwings.Discriminant linear analysis(DLA)was used to compare the time and frequency parameters of the call types measured in Raven PRO.Also,lapwings’responses to intruders,alert and start distance,time of day,and latency,as well as the effects of flock size and distance to cover were examined.About 48%of all calls was correctly classified by DLA.The best predictors of call type for the lapwings were maximum frequency and high frequency.Both alarm and mobbing calls were elicited by African Wattled Lapwings to dogs and humans.Mobbing calls were elicited to intruders by the Spur-winged Lapwings.Alert distance was positively associated with start distance,and differed between morning and evening in both lapwings.With scarce information from tropical Africa,this study put in perspective vocal and antipredator behavior of lapwing species in Africa.展开更多
The Sociable Lapwing(Vanellus gregarius) was recently categorized as Critically Endangered by the IUCN due to a strong decline and overall range contraction.Until now the only published Chinese record of the species w...The Sociable Lapwing(Vanellus gregarius) was recently categorized as Critically Endangered by the IUCN due to a strong decline and overall range contraction.Until now the only published Chinese record of the species was a vagrant sighting in 1998.We reviewed reports and historic literature from a German ornithological expedition in 1876,which reported the species to be a breeding bird in Xinjiang,western China in the second half of the 19th century.According to local expertise,the species seems since to have become extinct in Xinjiang,but surveys are suggested to clarify its current status.展开更多
Electronic structure and magnetic properties of wurtzite ZnO semiconductor doped with rare earth （RE=La, Ce, Pr, Pm, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb） atoms were studied using spin-polarized density functio...Electronic structure and magnetic properties of wurtzite ZnO semiconductor doped with rare earth （RE=La, Ce, Pr, Pm, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb） atoms were studied using spin-polarized density functional theory based on the full-potential linear augmented plane wave （FP-LAPW） method as implemented in the Wien2k code. In this approach the generalized gradient approximation （GGA） was used for the exchange-correlation （XC） potential. Our results showed that the substitution of RE ions in ZnO induced spins polarized localized states in the band gap. Moreover, the studied DMSs compounds retained half metallicity at dopant concentration x=0.625%for most of the studied elements, with 100%spin polarization at the Fermi level （EF）. The total magnetic moments of these compounds existed due to RE 4f states present at EF, while small induced magnetic moments existed on other non-magnetic atoms as well. Finally, the energy difference between far and near configurations was investigated. It was found that the room temperature ferromagnetism was possible for RE-doped ZnO at near configuration. Since the RE-RE separation was long enough （far configuration） for magnetic coupling, the system became paramagnetic or antiferromagnetic ground state.展开更多
The electronic structures of the titanium dioxide（TiO2） doped with V and Fe were analyzed by using first-principle calculations based on the density functional theory（DFT） with the full potential linearized augmen...The electronic structures of the titanium dioxide（TiO2） doped with V and Fe were analyzed by using first-principle calculations based on the density functional theory（DFT） with the full potential linearized augmented plane wave method （FP-LAPW）. The fully optimized structure and the relaxation introduced by impurity were obtained by minimizing the total energy and atomic forces. The unit cell of the V-doped anatase TiO2 is smaller than that of the non-doped one, but for the Fe-doped one, the case is just the opposite. It is found that the apical Ti-O and impurity-O bond lengths of the V/Fe-doped anatase TiO2 are greater than those of the non-doped structure, but smaller for the equatorial bond length. Through the band structures and the density of states, the V-doped TiO2 is shown to be a kind of half-metal, while the Fe-doped TiO2 a kind of metal. The magnetic moments of the V/Fe-doped system are mainly generated by the dopants. The results may be helpful for us to understand the experimental outcome of this system.展开更多
The mechanical, electronic and magnetic properties of non-magnetic MgTe and ferro-magnetic （FM） Mgo.75 TM025 Te （TM = Fe, Co, Ni） in the zinc-blende phase are studied by ab-initio calculations for the first time. ...The mechanical, electronic and magnetic properties of non-magnetic MgTe and ferro-magnetic （FM） Mgo.75 TM025 Te （TM = Fe, Co, Ni） in the zinc-blende phase are studied by ab-initio calculations for the first time. We use the generalized gradient approximation functional for computing the structural stability, and mechanical properties, while the modified Becke and Johnson local （spin） density approximation （mBJLDA） is utilized for determining the electronic and magnetic properties. By comparing the energies of non-magnetic and FM calculations, we find that the compounds are stable in the FM phase, which is confirmed by their structural stabilities in terms of enthalpy of formation. Detailed descriptions of elastic properties of Mgo.75TMo.25Te alloys in the FM phase are also presented. For electronic properties, the spin- polarized electronic band structures and density of states are computed, showing that these compounds are direct bandgap materials with strong hybridizations of TM 3d states and Te p states. Further, the ferromagnetism is discussed in terms of the Zener free electron model, RKKY model and double exchange model. The charge density contours in the （110） plane are calculated to study bonding properties. The spin exchange splitting and crystal field splitting energies are also calculated. The distribution of electron spin density is employed in computing the magnetic moments appearing at the magnetic sites （Fe, Co, Ni）, as well as at the non-magnetic sites （Mg, Te）. It is found that the p-d hybridization causes not only magnetic moments on the magnetic sites but also induces negligibly small magnetic moments at the non-magnetic sites.展开更多
基金funding(No.217)from the A.P.Leventis Foundation Scholarship(to F.R.J).
文摘Predation is an important source of natural selection on prey species and has resulted in adaptations such as antipredator vocal signals,which can alert others to the presence of predators and solicit cooperative attack.Although vocal alarm signals of birds have been well studied,they are poorly known in tropical African species.To address this lack of information,the antipredatory signals and responses of two lapwings(Wattled Lapwing Vanellus senegallus and Spur-winged Lapwing Vanellus spinosus)to potential predators were investigated using data collected from focal observation,distance measurements,focal recordings,and playback experiment.The lapwing calls elicited to predators were classified as alarm or mobbing calls based on whether the calls elicited alert behavior or attack from other lapwings.Discriminant linear analysis(DLA)was used to compare the time and frequency parameters of the call types measured in Raven PRO.Also,lapwings’responses to intruders,alert and start distance,time of day,and latency,as well as the effects of flock size and distance to cover were examined.About 48%of all calls was correctly classified by DLA.The best predictors of call type for the lapwings were maximum frequency and high frequency.Both alarm and mobbing calls were elicited by African Wattled Lapwings to dogs and humans.Mobbing calls were elicited to intruders by the Spur-winged Lapwings.Alert distance was positively associated with start distance,and differed between morning and evening in both lapwings.With scarce information from tropical Africa,this study put in perspective vocal and antipredator behavior of lapwing species in Africa.
基金funded by the Darwin Initiative of the UK government and the Royal Society for the Protection of Birds (RSPB)support from Swarovski optics, The Rufford Foundation and Deutsche Ornithologen-Gesellschaft (DO-G)
文摘The Sociable Lapwing(Vanellus gregarius) was recently categorized as Critically Endangered by the IUCN due to a strong decline and overall range contraction.Until now the only published Chinese record of the species was a vagrant sighting in 1998.We reviewed reports and historic literature from a German ornithological expedition in 1876,which reported the species to be a breeding bird in Xinjiang,western China in the second half of the 19th century.According to local expertise,the species seems since to have become extinct in Xinjiang,but surveys are suggested to clarify its current status.
文摘Electronic structure and magnetic properties of wurtzite ZnO semiconductor doped with rare earth （RE=La, Ce, Pr, Pm, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb） atoms were studied using spin-polarized density functional theory based on the full-potential linear augmented plane wave （FP-LAPW） method as implemented in the Wien2k code. In this approach the generalized gradient approximation （GGA） was used for the exchange-correlation （XC） potential. Our results showed that the substitution of RE ions in ZnO induced spins polarized localized states in the band gap. Moreover, the studied DMSs compounds retained half metallicity at dopant concentration x=0.625%for most of the studied elements, with 100%spin polarization at the Fermi level （EF）. The total magnetic moments of these compounds existed due to RE 4f states present at EF, while small induced magnetic moments existed on other non-magnetic atoms as well. Finally, the energy difference between far and near configurations was investigated. It was found that the room temperature ferromagnetism was possible for RE-doped ZnO at near configuration. Since the RE-RE separation was long enough （far configuration） for magnetic coupling, the system became paramagnetic or antiferromagnetic ground state.
基金National Natural Science Foundation of China (50541036)
文摘The electronic structures of the titanium dioxide（TiO2） doped with V and Fe were analyzed by using first-principle calculations based on the density functional theory（DFT） with the full potential linearized augmented plane wave method （FP-LAPW）. The fully optimized structure and the relaxation introduced by impurity were obtained by minimizing the total energy and atomic forces. The unit cell of the V-doped anatase TiO2 is smaller than that of the non-doped one, but for the Fe-doped one, the case is just the opposite. It is found that the apical Ti-O and impurity-O bond lengths of the V/Fe-doped anatase TiO2 are greater than those of the non-doped structure, but smaller for the equatorial bond length. Through the band structures and the density of states, the V-doped TiO2 is shown to be a kind of half-metal, while the Fe-doped TiO2 a kind of metal. The magnetic moments of the V/Fe-doped system are mainly generated by the dopants. The results may be helpful for us to understand the experimental outcome of this system.
基金the Deanship of Scientific Research at King Saud University for funding this Prolific Research Group (PRG-1436-26)
文摘The mechanical, electronic and magnetic properties of non-magnetic MgTe and ferro-magnetic （FM） Mgo.75 TM025 Te （TM = Fe, Co, Ni） in the zinc-blende phase are studied by ab-initio calculations for the first time. We use the generalized gradient approximation functional for computing the structural stability, and mechanical properties, while the modified Becke and Johnson local （spin） density approximation （mBJLDA） is utilized for determining the electronic and magnetic properties. By comparing the energies of non-magnetic and FM calculations, we find that the compounds are stable in the FM phase, which is confirmed by their structural stabilities in terms of enthalpy of formation. Detailed descriptions of elastic properties of Mgo.75TMo.25Te alloys in the FM phase are also presented. For electronic properties, the spin- polarized electronic band structures and density of states are computed, showing that these compounds are direct bandgap materials with strong hybridizations of TM 3d states and Te p states. Further, the ferromagnetism is discussed in terms of the Zener free electron model, RKKY model and double exchange model. The charge density contours in the （110） plane are calculated to study bonding properties. The spin exchange splitting and crystal field splitting energies are also calculated. The distribution of electron spin density is employed in computing the magnetic moments appearing at the magnetic sites （Fe, Co, Ni）, as well as at the non-magnetic sites （Mg, Te）. It is found that the p-d hybridization causes not only magnetic moments on the magnetic sites but also induces negligibly small magnetic moments at the non-magnetic sites.
